This invention relates generally to a temperature sensitive seal assembly, and more particularly to a C-ring seal.
In many applications, a sealing assembly may be subject to extreme variations in temperature, for instance if a fire or explosion occurs and must be contained by the seal. While seals which can withstand severe temperature and pressure conditions do exist, it is often impractical in terms of the requirements of the normal operating environment to use such a seal for the relatively few occurrences of such severe conditions. Generally, high temperature seals are not resilient enough to be suitable as dynamic seals or in uses where a seal must be repeatedly created and removed, and resilient seals generally cannot withstand high temperatures.
For instance, a military tank door which is repeatedly opened and closed requires a "soft" seal, made of Teflon.RTM. or an elastomer, during normal operations, but also requires a seal which can withstand the occasional severe conditions mentioned above, when they occur.
In another application, a valve through which inflammable fluids pass must be "fire-safe" to prevent leakage when a fire destroys the "soft" seals. Prior fire-safe valves have utilized a redundant seal assembly consisting of a soft seal which, if destroyed by fire, is backed up by a high temperature metal seal or a Graphoil.RTM. packing. This back up seal is operative regardless of the temperature, and thus in addition to the wear of the back up seal during normal operation, the back up seal generates a large amount of friction, which is undesirable. Further, since the "soft" seal is not integral with the back up seal, a separate groove generally must be machined within the valve for each seal to be retained.
A special seal can also be advantageous in cryogenic applications. Typical materials used in cryogenic seals become brittle and contract as the temperature decreases, thus providing a weaker seal or even allowing clearance between the seal and its surrounding surfaces precisely when a strong seal is required. In this situation, a Teflon.RTM. seal, which normally becomes less effective as temperatures drop because of thermal shrinkage and stiffening, could still be operative at cryogenic temperatures if a greater biasing force were applied to force it into sealing engagement with the surrounding surfaces. However, prior biasing elements will also contract and become less effective at cryogenic temperatures, instead of providing a greater biasing force.
Thus, a need exists for a self-energizing seal which is able to withstand and be effective under severe temperature conditions.